Solar energy collector systems are generally one of two types. They are flat panel collector systems using a radiant energy absorbing fluid behind the transparent cover of the collector panel or they are optical concentration systems which use lens or mirror optics to concentrate the incident radiation on to a smaller area collector tube or other absorber which contains the working energy absorbing fluid. In general the flat panel collectors are much less costly to manufacture and they do not require tracking of the sun for good efficiency. They generally do not provide high fluid temperatures and are not suitable for generation of shaft power. The optical concentrator type of solar collector is usually fairly expensive to manufacture as compared with the flat panel and, for good efficiency, should be tracked to follow the sun. The tracking system adds to the cost and complexity of the system and reduces the reliability. The optical concentrator units do have the advantage that they do generate temperatures and are capable of heating the collector fluid to temperatures which are capable of generating substantial amounts of shaft power.
The present invention deals with a collector panel which combines the best features of the two types described and which is capable of producing working fluid temperatures high enough to generate shaft power. By the use of a novel working fluid composition a large amount of energy can be stored per unit of mass by a latent heat mechanism and released isothermally at an elevated temperature which provides for efficient energy release to generate shaft work in a heat engine.